In a tumbling mill having a grinding chamber which is circular in cross-section, the grinding elements are entrained along the periphery of the grinding chamber in the direction of rotation, specifically in a direction which is tangential to the cross-section. This is accomplished by undulations or ribs or the like. In addition to said entraining action, no entraining action is exerted on the grinding elements by centrifugal force. Besides, the circular cross-section of the grinding chamber does not result in a variation of the angle of separation at which the grinding elements enter their parabolic trajectory. This is one of the causes for the poor disintegration efficiency of such tumbling mills having a grinding chamber which is circular in cross-section. This poor disintegration efficiency is due to the fact that the small turbulence in the space occupied by the grinding elements results in a reduced number of fracturing events to which the material being ground is subjected. In a tube mill having a grinding chamber which is quadrangular in cross-section and has corners which are rounded along arcs of a circle, as is known, e.g., from Swiss Patent Specification No. 422,488, the variaton of the entraining component of force exerted on the grinding elements as a result of centrifugal force is relatively small at the corners. To increase the variation of that entraining component of force and the variation of the angle of separation, it is known to decrease the radius of curvature at the corners although this results in a great decrease of the volume of the grinding chamber compared to the conventional grinding chamber which is circular in cross-section and in extreme cases the throughput capacity of the mill may be reduced. Another undesired result of the smaller radius of curvature at the corners resides in that higher spacers are required for the grinding plates and the associated fasteners must be longer.
A further disadvantage resides in the heavy wear. Owing to a strong sliding movement between the smooth liner and the grinding elements, this wear is particularly heavy at the transition between the trailing end of the rounded corner and the straight side of the square because the radial acceleration is discontinuous there.
It is an object of the invention to increase the variation of the angle of separation and thus to increase the turbulence in the grinding chamber by an increase of the variation of the entraining component of force adjacent to the corners, also to reduce the irregular wear and to increase the service life of the liner plates, to provide a more desirable structure, which permits the use of more uniform liner plates, and to limit the height of the spacers for the liner plates and the length of the fastening screws.
Finally it is an object of the invention so to design the internal fixtures of the tumbuling mill that the liner plates and the spacers for such plates can be replaced individually.